Data from: Interactions among predators and plant specificity protects herbivores from top predators

The worldwide loss of top predators from natural and agricultural systems
has heightened the need to understand how important they are in
controlling herbivore abundance. The effect of top predators on herbivore
species is likely to depend on 1) the importance of the consumption of
intermediate predators by top predators (intra-guild predation; IGP), but
also on 2) plant specificity by herbivores, because specialists may defend
themselves better (enemy-free space; EFS). Insectivorous birds, as top
predators, are generally known to effectively control herbivorous insects,
despite also consuming intermediate predators such as spiders, but how
this effect varies among herbivore species in relation to the cascading
effects of IGP and EFS is not known. To explore this, we excluded birds
from natural fynbos vegetation in South Africa using large netted cages
and recorded changes in abundance relative to control plots for 199
plant-dwelling intermediate predator and 341 herbivore morpho-species that
varied in their estimated plant specificity. We found a strong negative
effect of birds on the total abundance of all intermediate predators, with
especially clear effects on spiders (strong IGP). In contrast with
previous studies, which document a negative effect of birds on herbivores,
we found an overall neutral effect of birds on herbivore abundance, but
the effect varied among species: some species were negatively affected by
birds, suggesting that they were mainly consumed by birds, whereas others,
likely released from spiders by IGP, were positively affected. Some
species were also effectively neutrally affected by birds. These tended to
be more specialized to plants compared to the other species, which may
imply that some plant specialists benefited from protection provided by
EFS from both birds and spiders. These results suggest that the response
of herbivore species to top predators may depend on cascading effects of
interactions among predators and on their degree of plant specificity.